quantumcloud509 said:
2.) Build Hobby King Prismatic pack, although just from your picture and description, I must say, I don't get it. I know for a fact that I dont want to mess with 6s+6s+4s.
Okay, will keep it simpler, assuming that you want a 12S pack instead of a 20S pack.
Since 12S packs are rare and expensive, we want to build it out of a 6S + 6S.
Option one is that you get a series connector like this:
It basically takes the negative of one battery, and connects it to the positive of the next, then takes the most positive and most negative of the whole setup, and you get a voltage equal to the sum of the two batteries. In this case, let's call it 25.2v + 25.2v = 50.4v battery
However, when it comes time to charging, the battery has 2 x JST-6S ports, so you will have effectively two batteries that aren't talking to each other or the charger. Let's say the charger forces 50.4v down the joint plug. You would hope both batteries were 25.2 But due to variations in manufacturing and environment, it's possible that the voltages start drifting. It could be one is 25.1, and the other 25.3. Not a big problem. But what happens if over time, one is 24.0 and the other 26.4? One will be under capacity, and the other being damaged from over charge. Let it go long enough and you have a nice puffy battery at best, and a fireball at worst.
Within each 6S, the balancer will make sure the cells is balanced, but between batteries, the voltages can vary.
You can get around this by charging each battery as 6S instead of the two batteries as 12S, but that's just annoying.
All that to explain why I prefer 20S instead of 6S+6S+4S... Here we go.
Now, instead of using that serial Y connector, I directly join the most positive cell of the first battery to the most negative cell of the second battery. A few less joins to worry about, and less resistance.
I also remove the 2 x JST-6S, and replace it with 1 x JST-12S and by a BMS that can monitor all 12 Cells. This way, if there's any unbalance, the BMS can know about it, and balance the whole thing properly.
Result? Pretty much a set and forget system (as long as you can trust your equipment), no looms or harnesses, no need to take anything apart to charge, etc.
It's really not as difficult as I make it sound. I don't know how to explain it better without actually doing it and showing you a video, and I don't have any plans to make new batteries in the near future. Sorry.
quantumcloud509 said:
7500w does sound shaky to run through a chain drive, even on my BBSxx fat bike I was running a KMC Kool Knight half link which made a huge difference by the way. I have another ebuild Im going to do after this Big Dummy, on a Surly Long Haul Trucker where I spliced the rear triangle and installed a gates belt drive and nuvinci 360 internal gear hub. The Dummy will eventually be getting a belt drive as well, but first I will have to have the motor, so that I can do some measurements.
I'm not against mid-drives, and in fact I'm intending to build one eventually. But I want to do mine with a belt drive and an internally geared hub. Reduce some of the maintenance required and increase safety. Unfortunately belt drives need specific frames, so I need to pick my donor bike carefully.